Connector for assembling two riser segments, comprising an internal locking ring and removable pins

ABSTRACT

The present invention relates to a compact connector design with an internal locking ring ( 11 ). The connector according to the invention comprises a locking ring ( 11 ) allowing bayonet type connection on either side with two riser sections. Furthermore, the connector comprises at least one removable pin ( 12 ) for translationally blocking locking ring ( 11 ), notably upon locking and unlocking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application filed under 35U.S.C. § 371 of International Application No. PCT/EP2016/077754, filedNov. 15, 2016, designating the United States, which claims priority fromFrench Patent Application No. 15/62.605, filed Dec. 17, 2015, which arehereby incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the field of deepwater oil drilling andreservoir development. It concerns a riser connector.

BACKGROUND OF THE INVENTION

A drilling riser is made up of an assembly of tubular elements of lengthranging between 15 and 27 m (50 and 90 feet), assembled by connectors.The tubular elements generally consist of a main tube provided with aconnector at each end. Tubular auxiliary lines, also called peripherallines, commonly referred to as “kill line”, “choke line”, “booster line”and “hydraulic line”, allowing circulation of technical fluids, areprovided parallel to the main tube. The tubular elements are assembledon the drilling site, from a floater. The riser is lowered into thewater depth as the tubular elements are assembled, until it reaches thewellhead located on the sea bottom.

In the perspective of drilling at water depths that can reach 3500 m ormore, the weight of the riser becomes very penalizing. This phenomenonis increased by the fact that, for the same maximum working pressure,the length of the riser requires a larger inside diameter for theauxiliary lines, considering the necessity to limit pressure drops.

Besides, the necessity to decrease the riser assembly time is all themore critical since the water depth, and therefore the riser length, isgreat.

A riser intended for other applications, notably production, completionor workover, also consists of an assembly of tubular elements assembledby connectors.

Documents FR-2,925,105, FR-2,956,693 and FR-2,956,694 describe varioussolutions notably aiming to involve the auxiliary lines, together withthe main tube, in the taking up of the longitudinal stresses applied tothe riser. However, for the systems described in these patents,fastening of the auxiliary lines with respect to the main tube causestensile stresses in the auxiliary lines. In order to withstand thesetensile stresses, the auxiliary lines have great thickness values, whichgenerates an increase in the mass and size of the floats, and thereforein the cost of the riser. Another problem with these connectors concernsthe inspection and maintenance of the locking ring. Indeed, the lockingrings in the aforementioned patents are not fully removable. It istherefore not possible to inspect the entire locking ring.

To overcome this problem, patent applications WO-2015/071,411,WO-2015/169,560 and WO-2015/169,559 relate to connectors provided withlocking rings removable by means of two bayonet connections. However,these three connectors require a particular layout for the studs toprevent simultaneous disconnection of the ring with the two risersections.

The present invention describes a compact connector design with aninternal locking ring. The connector according to the inventioncomprises a locking ring allowing a bayonet type connection on eitherside with two riser sections. Besides, the connector comprises at leastone removable pin for translationally blocking the locking ring, notablyupon locking and unlocking. Thus, the connector according to theinvention is removable, and simultaneous removal of the ring with thetwo riser sections is prevented.

SUMMARY OF THE INVENTION

The invention relates to a connector for assembling two riser sections,comprising a first main tube element extended by a male connectorelement, a second main tube element extended by a female connectorelement, the male connector element fitting into said female connectorelement so as to connect said two main tube elements, said connectorcomprising means for locking said assembly that include a locking ring,said locking ring comprising a first and a second series of studs on theouter surface thereof and said male and female connector elementsrespectively comprising on the inner face thereof a third and a fourthseries of studs respectively cooperating with said first and secondseries of studs. Said locking means further comprise at least oneremovable pin arranged in said locking ring and cooperating with saidmale connector element so as to translationally block said locking ringwith respect to said male connector element.

According to one embodiment, the studs of the first and second series ofstuds project over identical angular ranges.

Advantageously, said removable pin cooperates with a groove provided insaid male connector element or with a shoulder provided in said maleconnector element.

According to a design, said male connector element comprises an endpiece and a sleeve provided with said groove or said shoulder, saidsleeve being suited to be fitted into said female connector element.

Preferably, the sleeve is bolted to said end piece.

According to an implementation, each series of studs comprises at leastone row of studs, preferably two rows of studs.

According to a variant, the circumferential distributions of said studsof two consecutive rows of studs of the same series of studs arealternated.

According to a characteristic, at least one row of studs of a series ofstuds is inscribed in a different diameter than another row of saidseries of studs.

According to an embodiment of the invention, said rows of studs of atleast one series of studs are inscribed in identical diameters.

Advantageously, said locking means comprise a plurality of removablepins, preferably a number of removable pins corresponding to the numberof studs per row of studs.

According to a design, said removable pin is threaded and said removablepin is arranged in said locking ring by screwing.

According to an embodiment, said removable pin is arranged in saidlocking ring between said first and said second series of studs.

According to a variant embodiment, said series of studs comprise atleast three studs, preferably at least four studs.

According to an embodiment design, said male and female connectorelements are respectively provided with a flange for respective passageof a first and a second auxiliary tube element.

According to a first variant embodiment, said auxiliary tube elementsare fixedly secured to said flanges.

According to a second variant, one auxiliary tube element is secured toone of said flanges and the other auxiliary tube element is connected bya sliding pivot connection to the other one of said flanges, saidsliding pivot connection allowing a relative translational motionbetween said main tube element and said auxiliary tube element over alimited distance.

According to a third variant, said two auxiliary tube elements areconnected by a sliding pivot connection to said flanges.

According to an embodiment, a first axial clearance is provided betweensaid first series of studs and said third series of studs, and a secondaxial clearance is provided between said second series of studs and saidfourth series of studs.

Advantageously, said first and second axial clearances range between 0.5and 30 mm, preferably between 0.5 and 10 mm.

The present invention further relates to a riser comprising at least tworiser sections assembled by a connector according to one of the abovecharacteristics.

Furthermore, the invention relates to a method of assembling two risersections by means of a connector according to one of the abovecharacteristics. The following steps are therefore carried out:

-   -   a) inserting said locking ring into said male connector element,    -   b) inserting said removable pin into said locking ring,    -   c) inserting said locking ring into said female connector        element, and    -   d) locking said locking ring.

According to an implementation of the invention, the locking step iscarried out through relative rotation of said locking ring with respectto said main tube elements.

According to an embodiment of the invention, at least one insertion ofsaid locking ring into said male or female connector element is carriedout through relative translation of said locking ring with respect tosaid male or female connector element.

According to a variant embodiment, at least one insertion of saidlocking ring into said male or female connector element is carried outthrough at least a first relative translation, a first relative rotationand a second relative translation of said locking ring with respect tosaid male or female connector element.

Moreover, the invention relates to a method of disassembling two risersections assembled by means of a connector according to one of the abovecharacteristics, characterized in that the following steps are carriedout:

-   -   a) unlocking said locking ring,    -   b) removing a first main tube element from said locking ring,    -   c) removing said removable pin from said locking ring, and    -   d) removing said locking ring from the second main tube element.

According to an embodiment, the unlocking step is carried out throughrelative rotation of said locking ring with respect to said main tubeelements.

According to a variant embodiment, at least one removal of at least onemain tube element from said locking ring is carried out through relativetranslation of said locking ring with respect to said main tube element.

According to an implementation of the invention, at least one removal ofat least one main tube element from said locking ring is carried outthrough a first relative translation, a first relative rotation and asecond relative translation of the locking ring with respect to saidmain tube element.

Furthermore, the invention relates to the use of a riser according toone of the above characteristics for performing offshore well drillingor workover or production operations.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the system and of the method accordingto the invention will be clear from reading the description hereafter ofembodiments given by way of non limitative example, with reference tothe accompanying figures wherein:

FIG. 1 schematically shows a riser according to the invention,

FIG. 2 illustrates a riser section according to an embodiment of theinvention,

FIG. 3 illustrates the connector according to an embodiment of theinvention,

FIG. 4 is an enlarged view of the connector illustrated in FIG. 3,

FIG. 5 illustrates, in partial view, a male or female connector elementfor a connector according to an embodiment of the invention,

FIG. 6 illustrates a locking ring for a connector according to anembodiment of the invention,

FIGS. 7a and 7b illustrate two steps of disassembling the locking ringaccording to an embodiment of the invention, and

FIGS. 8a to 8d illustrate the distribution of the clearances for anembodiment of the invention, for the following steps respectively:approach, contacting the ring with the female connector element, lockingand tensioning.

DETAILED DESCRIPTION OF THE INVENTION

According to a non-limitative example embodiment, FIG. 1 schematicallyshows a riser 1 installed offshore. Riser 1 extends well P and itstretches from wellhead 2 to floater 3, a platform or a vessel forexample. Wellhead 2 is provided with a preventer commonly referred to as“B.O.P.” or “Blow-Out Preventer”. Riser 1 is made up of an assembly ofseveral sections 4 assembled end to end by connectors 5. Each sectionconsists of a main tube element 6 provided with at least one auxiliarytube element 7, also referred to as peripheral line. The auxiliary linesreferred to as kill lines or choke lines are used to provide well safetyduring control procedures relative to the inflow of fluids underpressure in the well. The line referred to as choke line is a safetyline carrying fluids (oil, water, gas) coming from the well in the eventof an inflow and driving them towards the choke manifold and the flare.The line referred to as kill line is a safety line enabling injectioninto the well of heavy fluids and cements allowing an otherwiseuncontrollable blowout to be stopped. The auxiliary line referred to asbooster line allows mud to be injected into the well in order toincrease the annulus velocity thereof and to prevent sedimentation ofthe cuttings; it is also used for replacing the mud contained in theriser by water prior to disconnection. The line referred to as hydraulicline allows the wellhead preventer to be controlled. Hydraulic linesallow the BOP safety devices (valves and accumulators) to be suppliedwith hydraulic fluid (glycol-laden distilled water) under pressure.

FIG. 2 diagrammatically shows a section 4 of the riser according to anembodiment of the invention. Section 4 comprises a main tube element 6whose axis forms the axis of the riser. Auxiliary tubes 7 make upauxiliary lines or tubes arranged parallel to the axis of the main tube.Auxiliary tube elements 7 have lengths substantially equal to the lengthof main tube element 6, generally ranging between 10 and 30 meters.There is at least one line 7 arranged on the periphery of the main tube.In FIG. 2, two lines 7 are schematically shown.

A connector 5 shown in FIG. 1 consists of two elements designated, withreference to FIG. 2, by female connector element 8 and male connectorelement 9. Connector elements 8 and 9 are mounted at the ends of maintube element 6. Female connector element 8 is secured to tube 6, forexample by welding, by screwing, by crimping or by clamping linkage.Male connector element 9 is secured to tube 6, for example by welding,by screwing, by crimping or by clamping linkage. For this illustratedexample embodiment, the assembly of male connector element 9 with afemale connector element 8 of another section forms connector 5 thattransmits stresses from a riser section to the next section, notably thelongitudinal stresses undergone by the riser.

The connector according to the invention is suited for a drilling riser,for example as described in connection with FIGS. 1 and 2, but theconnector according to the invention can also be suited for acompletion, workover or production riser, whose particular feature isnotably to have no auxiliary line. According to the invention, theconnector comprises:

-   -   a first main tube element extended by a male connector element,        which can be optionally provided with guide means (a male flange        for example) for passage of an auxiliary tube element (in cases        where the riser comprises at least one auxiliary line),    -   a second main tube element extended by a female connector        element, which can be optionally provided with guide means (a        female flange for example) for passage of an auxiliary tube        element (in cases where the riser comprises at least one        auxiliary line), the male connector element fitting into the        female connector element so as to connect the main tube elements        and the auxiliary tube elements,    -   optionally a first auxiliary tube element passing through the        male flange,    -   optionally a second auxiliary tube element passing through the        female flange, and    -   means for locking the assembly, comprising:        -   a locking ring, referred to as internal locking ring,            arranged within the male and female connector elements, the            locking ring comprising, on the outer face thereof, a first            series and a second series of studs suited to cooperate with            a third series and a fourth series of studs respectively            arranged on inner surfaces of the male and female connector            elements, and        -   at least one removable pin, the removable pin being arranged            in the locking ring and suited to cooperate with the male            connector element so as to translationally block the locking            ring with respect to the male connector element, and the            removable pin can notably cooperate with a groove provided            in the locking ring, or notably with a shoulder provided in            the locking ring.

Thus, by means of the four series of studs, two bayonet type connectionsare formed: a first one between the locking ring and the male connectorelement, and a second one between the locking ring and the femaleconnector element. The locking ring is thus made removable with respectto the male and female connector elements, which allows inspection andmaintenance thereof.

Arranging the ring inside the male and female connector elements allowsto reduce the size of the connector and thus provides connectorcompactness.

The removable pin is suited to cooperate with the male connector elementin order to prevent axial translation of the locking ring with the maleconnector element. The removable pin can notably cooperate with a grooveprovided in the locking ring or with a shoulder provided in the lockingring. Thus, upon assembly of two sections by means of the connector, itis possible to prevent removal of the locking ring, upon assembly ordisassembly of the female connector element. Advantageously, theremovable pin, once mounted in the locking ring, projects on the innerpart of the locking ring. The projection distance of the removable pincan be equivalent to the depth of the groove or of the shoulder providedin the male connector element. The removable pin can be mounted on theouter surface of the locking ring. The removable pin can be inserted inthe locking ring once the first assembly (locking ring and a maleconnector element) is assembled but not locked. The removable pin can beremoved from the locking ring once the second assembly (locking ring andfemale connector element) is disassembled and the first assembly(locking ring and male connector element) is unlocked.

According to an embodiment of the invention, the studs of the first andsecond series of studs (and a fortiori of the third and fourth series ofstuds) project over identical angular ranges. The angular range of astud is understood to be the angle formed by the disc portion occupiedby the stud over the diameter in which it is inscribed. For example, ifa series of studs comprises studs representing each one sixth of a disc,the angular range of the stud is 60°. Thus, with this design, lockingand unlocking of the locking ring with respect to the two connectorelements can result from a single rotation and become simultaneous. Thelocking ring is therefore driven in rotation only between two angularpositions.

According to a first implementation of the invention, thecircumferential distributions of the first and second series of studsare symmetrical with respect to a radial plane passing through the twoseries of studs. In other words, the studs of the first and secondseries of studs face each other (are aligned). Thus, the locking ringcan have a symmetry plane, which can facilitate the design thereof.According to a second implementation of the invention, thecircumferential distributions of the first and second series of studsare opposed: the circumferential distribution of the second series ofstuds is offset with respect to the first series of studs, by an anglecorresponding to the angular range of a stud. In other words, the studsof a series face the intervals of the other series. According to a thirdimplementation of the invention, the circumferential distributions ofthe studs of the first and second series are offset in relation to oneanother, by an angle corresponding to half the angular range of a stud(or any other angle).

Alternatively, the studs of the first and second series of studs (and afortiori of the third and fourth series of studs) project over differentangular ranges. Thus, unlocking of the two bayonet connections isachieved through distinct rotations.

Preferably, the locking ring can be made in a single piece.

The connector can be designed and dimensioned so as to meet thespecifications mentioned by the API 16 R and API 2 RD standards editedby the American Petroleum Institute.

The various embodiments described above and hereafter can be combined soas to combine the effects thereof.

According to an embodiment of the invention, the male connector elementcan be formed with an end piece and a sleeve. The end piece comprises afirst end intended to be fixed to a main tube element and a second endcomprising, on the inner surface thereof, the third series of studs,which is intended to cooperate with the locking ring. The sleeve abutsagainst a shoulder of the end piece and it is fixed in the end piece, atone end of the sleeve, by bolting for example. On the other side, thesleeve projects so as to fit into the female connector element. Thesleeve has a substantially cylindrical shape. The end piece, on the partthereof used for connection with the locking ring, comprises an insidediameter greater than the outside diameter of the locking ring. Thesleeve comprises an outside diameter substantially corresponding to theinside diameter of the locking ring. The sleeve comprises, on the outersurface thereof, the groove intended to receive at least one removablepin projecting on the inner surface of the locking ring. In this case,the locking ring is inserted between the sleeve and the third and fourthseries of studs.

According to a design of the invention, the removable pin can bethreaded. It can then be mounted in the locking ring by screwing. Thisdesign enables fast assembly of the removable pin. In order to allowease of assembly, the removable pin can be hollow to enable manipulationthereof with a tool.

According to a feature of the invention, the pin can have any shape,notably cylindrical (of circular or elliptical section), conical,parallelepipedic (of rectangular or square section), etc.

The removable pin can be arranged in the locking ring between the firstand second series of studs. Thus, the removable pin can be substantiallyin the centre of the locking ring.

The groove provided in the male connector element (or, as the case maybe, in the sleeve) can advantageously have a depth and a width greaterthan the dimensions of the removable pin, so as to allow the removablepin to slide in the groove, in particular to enable rotation of thelocking ring when the removable pin is mounted.

According to an embodiment of the invention, each series of studs cancomprise at least one row of studs. A row of studs is understood to be acircumferential distribution of the studs. Each row of studs has analternation of projecting studs and of void spaces (intervals), thesevoid spaces allowing passage of the corresponding studs of the series ofstuds with which the row of studs cooperates.

According to an implementation of the invention, the series of studs cancomprise a plurality of rows of studs, in particular two or three rowsof studs. The plurality of rows of studs allows the axial loads on thestuds to be decreased, which allows to limit the mechanical fatigue ofthe studs.

According to a possible design, each series of studs comprises a singlerow of studs. According to a first alternative, each series of studscomprises two rows of studs. According to a second alternative, eachseries of studs comprises three rows of studs. According to a thirdalternative, two of the four series of studs comprise one row of studsand the other two series comprise two rows of studs. According to afourth alternative, two of the four series of studs comprise two rows ofstuds and the other two series comprise three rows of studs.

In cases where a series of studs comprises several rows of studs, thenthe rows of studs can be inscribed in different diameters. This designallows to pass the row of studs of smaller diameter, and it is thuspossible to lock and unlock the bayonet connection with a singlerotation.

In cases where a series of studs comprises several rows of studs, thenthe rows of studs can be inscribed in identical diameters. This designrequires insertion and locking of the bayonet connection by a relativemotion consisting of a first translation, a first rotation, a secondtranslation and a second rotation. This design thus allows betterconnection security because it allows unwanted disconnection to beavoided.

Each row of studs comprises a plurality of studs evenly distributed overa diameter. Advantageously, the studs of the various rows can bearranged to allow 360° locking. According to a design, the rows of studscan comprise three studs having an angular range of 60°, or 40°.According to an alternative, the rows of studs can comprise four studshaving an angular range of 45°, or 30°. According to an alternative, therows of studs can comprise five studs having an angular range of 36°, or24°. According to another alternative, the rows of studs can comprisesix studs having an angular range of 30°, or 20°. According to analternative, the rows of studs can comprise eight studs having anangular range of 22.5°, or 15°. In order to have the studs projectingover identical angular ranges, all the rows of all the series of studscan comprise the same number of studs.

According to an embodiment of the invention, the locking means comprisea plurality of removable pins. It is thus possible to distribute thestresses among the removable pins. For this embodiment, a number ofremovable pins corresponding to the number of studs of the third seriesor of the fourth series of studs (a fortiori of the first or of thethird series of studs) can be provided. Alternatively, a number ofremovable pins substantially corresponding to half the number of studsof the third or of the fourth series of studs can be provided. Thisalternative allows to obtain a compromise between the number of pins andthe stresses exerted on the pins.

FIG. 3 illustrates, by way of non limitative example, a connectoraccording to an embodiment of the invention, the connector assemblingtwo riser sections. FIG. 3 corresponds to a sectional view of theconnector. In this figure, only one side of the sectional view is shown,the second side can be deduced by axial symmetry. The axis of thesections and of the connector is represented horizontally. In thefigure, the flanges and auxiliary tube elements 7 are shown, but theyare not necessary to the connector according to the invention. A maleconnector element 9 is fitted in a female connector element 8. Maleconnector element 9 comprises an end piece 20 and a sleeve 21. Lockingmeans lock the assembly. The locking means comprise a locking ring 11.Locking ring 11 comprises, on the outer face thereof, a first series ofstuds 15 and a second series of studs 16. First series of studs 15cooperates with a third series of studs 17 arranged on the inner face ofmale connector element 9, in particular of end piece 20. Second seriesof studs 16 cooperates with a fourth series of studs 18 arranged on theinner face of female connector element 8. Besides, the locking meanscomprise at least one removable pin 12. Removable pin 12 is mounted inlocking ring 11 so as to project on the inner part thereof. Removablepin 12 is suited to cooperate with a groove provided in sleeve 21. Theremovable pin 12 illustrated has a substantially cylindrical shape witha shoulder. The shoulder allows precise positioning of removable pin 12in the locking ring. Furthermore, the removable pin 12 illustrated ishollow for passage of a tool allowing setting thereof and/or foractuating locking ring 11, by means of an actuating bar for example.

FIG. 4 shows, by way of non limitative example, an enlarged view of FIG.3 in the region of removable pin 12. Removable pin 12 is mounted inlocking ring 11. It is located between the first series of studs and thesecond series of studs. Furthermore, the removable pin is located in aninterval between male connector element 9 and female connector element8. Removable pin 12 projects into locking ring 11 and it can slide in agroove 19 provided in sleeve 21. The dimensions (width, depth) of groove19 are larger than the dimensions (diameter and length for example) ofthe end of the removable pin so as to allow removable pin 12 to slide inthe groove.

FIG. 5 illustrates, by way of non limitative example, in a sectionalview, an end piece 20 of a male connector element 9 for the embodimentof FIG. 3. In this figure, the sleeve that is intended to be fixed toend piece 20 is not shown. End piece 20 is a substantially cylindricalpart comprising a first end 22 intended to be fixed to a main tubeelement. End piece 20 of male connector element 9 comprises, on theinner face thereof, a third series of studs consisting of two rows ofstuds 17A and 17B. Row 17A is the most central in the connector.According to the embodiment illustrated, each row of studs 17A, 17Bcomprises four studs having an angular range of 45°. The two rows ofstuds 17A, 17B are inscribed in different diameters. Thus, insertion andlocking in the locking ring (and, conversely, unlocking and removal) isallowed through a single translation. Furthermore, the circumferentialdistributions of the studs of rows 17A, 17B are alternated: the studs ofrow 17A face (are aligned with) the intervals between two studs of row17B and vice versa. This figure schematically shows, by way of nonlimitative example, the shape of the flange allowing passage ofauxiliary tube elements.

The female connector element can be identical to end piece 20 shown inFIG. 5. In this case, it comprises a first end intended for a secondmain tube element, and two rows of studs forming the fourth series ofstuds. This embodiment allows standardization of the connector elements(part adaptable to the male or female connector element), whichfacilitates the manufacture thereof.

FIG. 6 illustrates, by way of non limitative example, a locking ring 11for the embodiment of FIG. 3. Locking ring 11 is a substantiallycylindrical part. Locking ring 11 comprises, on the outer surfacethereof, a first series of studs 15 and a second series of studs 16.First series of studs 15 is suited to cooperate with the third series ofstuds of the male connector element. Second series of studs 16 is suitedto cooperate with the fourth series of studs of the female connectorelement. According to the embodiment illustrated, each series of studs15, 16 comprises two rows of studs 15A, 15B and 16A, 16B. Rows 15A and16A are the most central rows of studs. Each row of studs comprises fourstuds having an angular range of 45°. In the example illustrated, thestuds of the central rows of studs 15A, 16A are inscribed in smallerdiameters than the diameters of outer rows of studs 15B, 16B.Furthermore, the circumferential distributions of the studs of rows 15A,15B are alternated: the studs of row 15A face (are aligned with) theintervals between two studs of row 15B and vice versa. Similarly, thecircumferential distributions of the studs of rows 16A, 16B arealternated: the studs of row 16A face (are aligned with) the intervalsbetween two studs of row 16B and vice versa. Besides, for the embodimentillustrated, the circumferential distributions of the studs of the firstand third series are symmetrical with respect to a radial plane betweenthe first and third series of studs: the studs of row 15A face (arealigned with) the studs of row 16A, and the studs of row 15B face (arealigned with) the studs of row 16B. Locking ring 11 also comprises fourorifices 23 for passage of the removable pins.

When the riser is provided with at least one auxiliary line, the maleand female connector elements can comprise means for guiding theauxiliary tube elements. These guide means can be a flange (formed by anincrease in the diameter of the male and female connector elements forexample), a support (that can for example be fixed to the male andfemale connector elements), a guide plate (that can for example be fixedto the male and female connector elements) or any similar means. Theflange, the support and the plate can comprise at least one orifice forpassage of the auxiliary tube elements.

The connector according to the invention can be designed in such a waythat the auxiliary tube element can have a relative motion with respectto the main tube element. Therefore, the two auxiliary tube elements canbe mounted with a sliding pivot connection or a sliding connection inthe guide means (for example in a support on one side and in a guideplate on the other). In the present application, a sliding pivotconnection designates a link connecting a first solid to a second solid,the first solid can translate with respect to the second solid in thedirection of an axis and the first solid can pivot with respect to thesecond solid about this axis. Thus, the auxiliary line element can slideand pivot in the axial direction thereof with respect to the main tube,and the auxiliary line element cannot move freely in the radial andtangential directions. In the present application, a sliding connectiondesignates a link connecting a first solid to a second solid where thefirst solid can translate with respect to the second solid in thedirection of an axis. Thus, the auxiliary line element can slide in theaxial direction thereof with respect to the main tube.

In a variant, the connector according to the invention can be designedin such a way that the auxiliary tube element can have no relativemotion with the main tube element. The two auxiliary tube elements cantherefore be fixedly secured in the guide means, for example in the twoflanges. Thus, the axial stresses can be distributed among the main lineand the auxiliary lines.

Alternatively, the connector according to the invention can be designedin such a way that, on one side, the auxiliary tube element can have norelative motion with the main tube element and, on the other side, theauxiliary tube element can have a relative motion with the main tubeelement. The auxiliary tube element can therefore be fixedly secured toa first guide means, a flange for example, and it can be in slidingpivot connection with a second guide means, a flange for example. Therelative motion distance can be limited, for example by a clearanceadjustment means. In other words, the riser section comprises, at eachend thereof, connection means schematized in FIG. 2 that allow, on oneside, to axially connect an auxiliary line element 7 to main tube 6 and,on the other side, to form the sliding pivot connection betweenauxiliary line element 7 and main tube 6.

For the latter variant embodiment, the fixed connection between theauxiliary line element and the main line element is achieved at thefemale connector element, and the sliding pivot connection between theauxiliary line element and the main line element is achieved at the maleconnector element. Alternatively, the fixed connection between theauxiliary line element and the main line element is achieved at the maleconnector element, and the sliding pivot connection between theauxiliary line element and the main line element is achieved at thefemale connector element.

The auxiliary tubes undergo axial compressive stresses caused by theinternal/external pressure difference that generates an “end effect”applied onto the tube ends (for example, the auxiliary lines can undergopressures of the order of 1034 bars, i.e. 15,000 psi). Under suchpressures, the main tube elements lengthen and the auxiliary lineelements shorten until the clearance is zero. When the clearance becomeszero, all the lines lengthen identically. The main tube elements arelikely to lengthen because they have to take up, totally or partly, theweight of the riser and the weight of the drilling mud on the one hand,and the tension forces imposed on the riser to keep it substantiallyvertical on the other hand. In general, the main tube elements at thetop of the riser, i.e. close to the sea surface, are subjected tomaximum tension forces, hence maximum elongation. The auxiliary lineelements are likely to shorten under the effect of the differencebetween the internal pressure and the external pressure due to the fluidthey contain. Indeed, the fluid applies a pressure onto the ends of theauxiliary tube elements by imposing compressive stresses on theauxiliary tube elements. Furthermore, the radial deformation of the tubedue to the internal/external pressure difference causes shortening ofthe tube. In general, the elements at the foot of the riser, i.e. closeto the sea bed, undergo the maximum internal/external pressuredifference, therefore maximum shortening.

As long as the clearance is positive, the length of the auxiliary tubeelement and of the main tube element positioned at the same height canvary independently of one another. On the other hand, when the clearancebecomes zero, i.e. when the clearance adjustment means is in contactwith the flange, the auxiliary tube element and the corresponding maintube element 6 form a hyperstatic assembly: the auxiliary tube elementis secured to the main tube element on the one hand at fastening meansand, on the other hand, at the stop that is in contact with the flange.Therefore, the main tube element induces tension forces in the auxiliarytube element, and vice versa.

Thus, these connections allow to distribute the tension forces appliedonto each riser section among main tube 6 and the auxiliary lineelements. The integration according to the invention via theestablishment of clearance J allows to increase the contribution of themain tube and consequently to reduce the axial stresses in theperipheral lines. Reduction of the axial stresses in the peripherallines by means of this integration is beneficial for the dimensioning ofthe end pieces and the thickness of the auxiliary tubes.

Advantageously, the clearance is selected as a function of the length ofthe section; indeed, the deformations of the various lines depend on thelength thereof. For a conventional riser section of 75 or 90 ft (22.86 mand 27.43 m), the clearance can be set between 0 and 1.5 inch (0 andapproximately 38.1 mm). Preferably, the clearance can be selectedbetween 0.1 and 1 inch (2.54 and 25.4 mm) for optimal distribution ofthe stresses in the lines, allowing to generate a decrease in the massof the riser. Alternatively, the clearance can be selected between 0.1and 0.25 inch (2.54 and 6.35 mm). According to an alternative, theclearance can be selected between 0.25 and 1 inch (6.35 and 25.4 mm). Apreferred option providing a good compromise is a clearance ofapproximately 0.5 inch (12.7 mm) or 1 inch (25.4 mm).

According to an embodiment of the invention, the auxiliary tube elementsare tubes hooped by reinforcement wires such as glass, carbon or aramidfibers, coated with a polymer matrix. Thus, the resistance and theweight of the auxiliary lines are optimized. Indeed, the presentinvention is particularly well suited for hooped auxiliary tube elementsthat afford the advantage of reducing the steel thickness and thereforethe weight of the riser. The drawback of hooping, involving lowerflexural rigidity, is compensated by the clearance that allows bucklingof the auxiliary lines to be limited. Alternatively, the main tube andauxiliary tube elements can be made of metal alloy, for examplealuminium alloy or titanium alloy.

In order to facilitate mounting and to avoid jamming of the studs causedby wear, at least one axial clearance can be provided between aconnector element and the locking ring. Preferably, the axial clearanceis strictly positive.

According to an embodiment of the invention, an axial clearance isprovided between each connector element and the locking ring. Thus,problems linked to studs wear can be avoided, which facilitates handlingof the locking ring. The two axial clearances can be identical ordistinct. The axial clearances are distributed within the connectorthroughout the connector assembly, locking, unlocking, and tensioningsteps. For example, upon assembly, an axial clearance may exist betweenthe studs cooperating with one another and, once the connector lockedand tensioned, an axial clearance may exist between the ends of the twoconnector elements.

Each axial clearance, strictly positive, can range between 0.5 and 30mm, preferably between 0.5 and 10 mm. Above 30 mm, the technical effectrelative to the avoidance of jamming problems remains, however itinvolves an increase in size.

Besides, according to a design of the connector, the ring can comprisering rotation limiting means, stops for example, these means limiting arotation of the locking ring for an angle equal to the angular range ofthe studs.

Furthermore, according to a feature of the invention, the connector cancomprise means for blocking the locking ring in at least one position,notably in the locked position. These means can also allow to preventrotation of the ring with respect to the male or female element in theunlocked position. The locking ring blocking means allow to avoidunwanted unlocking of the locking ring.

According to a design of the invention, the locking ring can comprisehandling means external to the locking ring. These handling means allowthe locking ring to be rotated. For example, the handling means can be ahandling bar. According to a design, the handling means can be insertedin a pin.

Moreover, the present invention relates to a riser comprising at leasttwo riser sections assembled by a connector as described above. Theconnector can be made according to any combination of the embodimentsdescribed above: plurality of removable pins, plurality of rows ofstuds, rows of studs inscribed in identical or distinct diameters, axialclearances, etc.

Furthermore, the present invention relates to the use of such a riser(with any combination of the embodiments described above) for performingoffshore drilling, effluent production or wellbore workover operations.

Besides, the present invention relates to a method of assembling tworiser sections by means of a connector according to the invention. Thefollowing steps can be carried out for this method:

-   -   a) inserting the locking ring into the male connector element,        thus the first main tube element is positioned in the locking        ring without being locked,    -   b) inserting at least one removable pin into the locking ring        until it penetrates the groove of the male connector element,        thus the first main tube element is positioned in the locking        ring while being translationally blocked and it still has a        rotating motion, it is therefore not locked,    -   c) inserting the locking ring into the female connector element,        so that the male connector element fits into the female        connector element, thus the second main tube element is        positioned in the locking ring without being locked, and    -   d) locking the locking ring by rotating the locking ring, this        single rotation locks the two connector elements that have no        more relative motion with respect to the locking ring.

For step d), upon locking, rotation of the ring generates the respectivecooperation of the first and third series of studs, and of the secondand fourth series of studs. The rotation enabling simultaneous lockingof the two bayonet type connections is a rotation by an anglecorresponding to the angular range of the studs. For example, if theangular range of the studs is 36°, the locking rotation is a 36°rotation.

For step b), axial translation blocking of the first main tube elementwith respect to the locking ring is achieved in the two axial directionsby contact of the removable pin(s) with the groove.

The insertion steps consist in setting the locking ring in the connectorelement concerned, so that a single subsequent rotation allows theconnector to be locked.

In some cases, the insertion steps correspond to a single relativetranslation motion of the ring with respect to the connector element.This is for example the case when the series of studs concerned onlycomprises one row of studs, or when the series of studs concernedcomprises a plurality of rows of studs inscribed in different diameters.This translation allows the studs to be positioned for blocking thebayonet connection.

In other cases, the insertion steps correspond to a combined motioncomprising a first stage of translation, followed by a first rotation,then a second translation. These are relative motions between thelocking ring and the connector element concerned. It is for example thecase when the series of studs concerned comprises a plurality of rows ofstuds inscribed in identical diameters. The first two relative motionsallow to pass a first row of studs. The last translation stage allowsthe studs to be positioned for blocking the bayonet connection.

According to an embodiment of the invention, where several pins aremounted to cooperate with the studs of the male connector element, andwhere the first and the third series of studs comprise two rows of studsinscribed in different diameters, and the second and fourth series ofstuds comprise two rows of studs inscribed in different diameters, themethod can comprise the following steps:

-   -   a) inserting the locking ring into the male connector element,        by means of a single translation,    -   b) inserting the removable pins into the locking ring,    -   c) inserting the female connector element into the locking ring,        by means of a single translation, so that the male connector        element fits into the female connector element, and    -   d) locking the locking ring by rotating the locking ring.

Furthermore, the present invention relates to a method of disassemblingtwo riser sections assembled by means of a connector according to theinvention. This method can comprise the following steps:

-   -   a) unlocking the locking ring by rotating the locking ring, this        single rotation unlocks the two connector elements that can have        relative motions with respect to the locking ring,    -   b) removing the female connector element from the locking ring,        so as to release the engagement of the male connector element in        the female connector element, thus the female connector element        is extracted from the locking ring while the male connector        element is unlocked but translationally blocked in the locking        ring, notably by at least one removable pin,    -   c) removing at least one removable pin from the locking ring,        thus the male connector element is positioned in the locking        ring while being unlocked and moving freely, and    -   d) removing the locking ring from the male connector element,        thus the male connector element is extracted from the locking        ring.

For step a), upon unlocking, rotation of the ring releases therespective cooperation of the first and third series of studs, and ofthe second and fourth series of studs. The rotation enablingsimultaneous unlocking of the two bayonet type connections is a rotationby an angle corresponding to the angular range of the studs. Forexample, if the angular range of the studs is 36°, the unlockingrotation is a 36° rotation.

The removal steps consist in extracting the connector element concernedfrom the locking ring, from a position where the connector element ispositioned in the locking ring.

In some cases, the removal steps correspond to a single relativetranslation motion of the ring with respect to the connector element.This is for example the case when the series of studs concerned onlycomprises one row of studs, or when the series of studs concernedcomprises a plurality of rows of studs inscribed in different diameters.This translation allows the studs to be released from the bayonetconnection.

In other cases, the removal steps correspond to a combined motioncomprising a first stage of translation, followed by a first rotation,then a second translation. These are relative motions between thelocking ring and the connector element concerned. It is for example thecase when the series of studs concerned comprises a plurality of studsinscribed in identical diameters. The first translation stage allows thestuds of the second series of studs to be disengaged. The last tworelative motions allow to pass a first row of studs.

FIGS. 7a and 7b illustrate, by way of non limitative example, two stepsof the disassembling process. FIG. 7a corresponds to the step ofremoving removable pins 12. FIG. 7b corresponds to the step of removinglocking ring from male connector element 9. Prior to the removal ofremovable pins 12, the female connector element (not shown) has beenremoved. Locking ring 11 is then unlocked (the studs of the first andthird series of studs do not cooperate), and locking ring 11 is held onsleeve 21 of male connector element 9 by removable pins 12. Removingremovable pins 12 enables relative translational displacement of lockingring 11 (FIG. 7b ) with respect to the male connector element. Thisrelative translation allows locking ring 11 to be removed, notably formaintenance or inspection thereof.

According to an embodiment of the invention, where several pins aremounted to cooperate with the studs of the male connector element, andwhere the first and the third series of studs comprise two rows of studsinscribed in different diameters, and the second and fourth series ofstuds comprise two rows of studs inscribed in different diameters, themethod comprises the following steps:

-   -   a) unlocking the locking ring by rotating the locking ring,    -   b) removing the female connector element from the locking ring        with a single motion of translation so as to release the        engagement of the male connector element in the female connector        element,    -   c) removing the removable pins in the locking ring, and    -   d) removing the locking ring from the male connector element, by        a single motion of translation.

For the embodiment where two axial clearances are provided on eitherside of the connector elements and the locking ring, the distribution ofthe axial clearances is illustrated in FIGS. 8a to 8d for variousassembly stages. These figures are sectional views similar to thesectional view of FIG. 3 and they illustrate stages of assembling maleconnector element 9 in female connector element 8 by means of a lockingring 11 and removable pins 12. The male connector element comprises asleeve 21.

Locking the connector can be achieved by means of the followingoperations:

1. Approach phase (FIG. 8a ): fitting male part 9 into female part 8.The studs of locking ring 11 pass between those of female element 8.

2. Fitting continues (FIG. 8b ), locking ring 11 comes into contact withthe inner part of female element 8. At this stage, a shoulder of femaleconnector element 8 is in contact C with the end of locking ring 11,while an axial clearance J2 exists between the studs of the second 16and fourth 18 series of studs, i.e. between central rows 16A and 18A andbetween outer rows 16B and 18B of the second and fourth series.

3. At the end of the fitting step (FIG. 8c ), sleeve 21 comes intocontact against a shoulder of female element 8. At this stage, an axialclearance J1 exists between studs of the first 15 and third 17 series ofstuds (i.e. between central rows 15A and 17A, and between outer rows 15Band 17B of the second and fourth series), a shoulder of female connectorelement 8 is in contact C with the end of locking ring 11, while anaxial clearance J2 exists between studs of the second 16 and fourth 18series of studs (i.e. between central rows 16A and 18A, and betweenouter rows 16B and 18B of the second and fourth series). At the end ofthis step, the connector is ready to be locked.

4. The rotation of the ring for locking (FIG. 8d ) causes the four rowsof teeth to coincide. It no longer risks being impeded because thesliding surface is located in a low-stress area. After locking,tensioning of the riser brings the teeth of the two bayonet systems intocontact. Thus, a contact C is achieved at the studs of the four seriesof studs and an axial clearance corresponding to the sum J1+J2 existsbetween the ends of sleeve 21 and a shoulder of female connector element8. Furthermore, a clearance J2 can be present between the end of lockingring 11 and a shoulder of female connector element 8.

For this example, axial clearances J1 and J2 are strictly positive, theycan be different or identical, and they can be 1, 2, 3, 4 or 5 mm.

The device according to the invention provides an attractive solutionfor rapidly and simply mounting a riser whose tension forces aredistributed among the auxiliary tube elements and the main tube. Indeed,connection of one riser section to another riser section is achieved ina single operation through rotation of the locking ring. This connectionallows to communicate and to seal the main tube element of a sectionwith that of the other section and, simultaneously, to communicate andto seal the auxiliary line elements of one of the sections with those ofthe other section.

For the embodiment where the riser comprises at least one auxiliaryline, the compact connector according to the invention allows tominimize the bending stresses in the flanges, and thus to reduce thedimensions of the flanges and to lighten the weight of the connectors.Besides, positioning the ring between the main tube element and theauxiliary tube elements allows to increase the strength of theconnector. Indeed, the ring holds the flanges and prevents bendingthereof. Moreover, this positioning allows to solve the problem ofauxiliary line fittings interference because the bending moments causedby offset axial forces have unlike signs. Furthermore, in lockedposition, the studs of the ring are engaged with the studs of the femaleconnector element that are positioned on the massive part of the femaleconnector element.

The invention claimed is:
 1. A connector for assembling two risersections, comprising a first main tube element extended by a maleconnector element, a second main tube element extended by a femaleconnector element, the male connector element fitting into the femaleconnector element so as to connect said two main tube elements, alocking ring for locking together the male connector element and thefemale connector element, the locking ring comprising a first and asecond series of studs on the outer surface thereof and the male andfemale connector elements respectively comprising on the inner facethereof a third and a fourth series of studs respectively cooperatingwith the first and second series of studs, and at least one removablepin arranged in the locking ring and cooperating with the male connectorelement so as to translationally block the locking ring with respect tothe male connector element, wherein the at least one removable pincooperates with a groove provided in the male connector element or witha shoulder provided in the male connector element.
 2. A connector asclaimed in claim 1, wherein the studs of the first and second series ofstuds project over identical angular ranges.
 3. A connector as claimedin claim 1, wherein the male connector element comprises an end pieceand a sleeve provided with the groove or the shoulder, the sleeve beingsuited to be fitted into the female connector element.
 4. A connector asclaimed in claim 3, wherein the sleeve is bolted to the end piece.
 5. Aconnector as claimed in claim 1, wherein each series of studs comprisesat least one row of studs.
 6. A connector as claimed in claim 5, whereineach series of studs comprises at least two rows of studs and thecircumferential distributions of the studs of two consecutive rows ofstuds of the same series of studs are alternated.
 7. A connector asclaimed in claim 5, wherein at least one row of studs of a series ofstuds is inscribed in a different diameter than another row of theseries of studs.
 8. A connector as claimed in claim 5, wherein the rowsof studs of at least one series of studs are inscribed in identicaldiameters.
 9. A connector as claimed in claim 5, wherein the lockingmeans comprise a plurality of removable pins.
 10. A connector as claimedclaim 1, wherein the removable pin is threaded and the removable pin isarranged in the locking ring by screwing.
 11. A connector as claimed inclaim 1, wherein the removable pin is arranged in the locking ringbetween the first and the second series of studs.
 12. A connector asclaimed in claim 1, wherein the series of studs comprise at least threestuds.
 13. A connector as claimed in claim 1, wherein the male andfemale connector elements are respectively provided with a flange forrespective passage of a first and a second auxiliary tube element.
 14. Aconnector as claimed in claim 13, wherein the auxiliary tube elementsare fixedly secured to the flanges.
 15. A connector as claimed in claim13, wherein one auxiliary tube element is secured to one of the flangesand the other auxiliary tube element is connected by a sliding pivotconnection to the other one of the flanges, the sliding pivot connectionallowing a relative translational motion between the main tube elementand the auxiliary tube element over a limited distance.
 16. A connectoras claimed in claim 13, wherein the two auxiliary tube elements areconnected by a sliding pivot connection to the flanges.
 17. A connectoras claimed in claim 1, wherein a first axial clearance is providedbetween the first series of studs and the third series of studs, and asecond axial clearance is provided between the second series of studsand the fourth series of studs.
 18. A connector as claimed in claim 17,wherein the first and second axial clearances range between 0.5 and 30mm.
 19. A riser comprising at least two riser sections assembled by aconnector as claimed in claim
 1. 20. A method for performing offshorewell drilling or workover or production operations, comprisingconnecting the riser as claimed in claim 19 to a wellhead.
 21. A methodof assembling two riser sections by means of a connector as claimed inclaim 1, wherein the following steps are carried out: a) inserting thelocking ring into the male connector element, b) inserting the removablepin into the locking ring, c) inserting the locking ring into the femaleconnector element, and d) locking the locking ring.
 22. A method asclaimed in claim 21, wherein the locking step is carried out throughrelative rotation of the locking ring with respect to the main tubeelements.
 23. A method as claimed in claim 21, wherein at least oneinsertion of the locking ring into the male or female connector elementis carried out through relative translation of the locking ring withrespect to the male or female connector element.
 24. A method as claimedin claim 21, wherein at least one insertion of the locking ring into themale or female connector element is carried out through at least a firstrelative translation, a first relative rotation and a second relativetranslation of the locking ring with respect to the male or femaleconnector element.
 25. A method of disassembling two riser sectionsassembled by means of a connector as claimed in claim 1, wherein thefollowing steps are carried out: a) unlocking the locking ring, b)removing a first main tube element from the locking ring, c) removingthe removable pin from the locking ring, and d) removing the lockingring from second main tube element.
 26. A method as claimed in claim 25,wherein the unlocking step is carried out through relative rotation ofthe locking ring with respect to the main tube elements.
 27. A method asclaimed in claim 25, wherein at least one removal of at least one maintube element from the locking ring is carried out through relativetranslation of locking ring with respect to the main tube element.
 28. Amethod as claimed in claim 25, wherein at least one removal of at leastone main tube element from the locking ring is carried out through afirst relative translation, a first relative rotation and a secondrelative translation of locking ring with respect to the main tubeelement.
 29. A connector as claimed in claim 1, wherein the at least oneremovable pin cooperates with a groove provided in the male connectorelement.
 30. A connector as claimed in claim 1, wherein the at least oneremovable pin cooperates with a shoulder provided in the male connectorelement.